I think the number one factor for determining the success of your PPC campaign is conversion.
The importance of conversion for PPC
Other factors are important too, but let's be realistic, you can be running the slickest and most cost effective PPC campaign in the history of Adwords, but if that traffic you're purchasing is not converting into revenue, or fulfilling some other objective, then it's time to reconsider the keywords you're bidding for, the properties you are displaying on, or the demographic you are targeting.
Syncing up your Google Adwords account with your Google Analytics account is usually the easiest way to track how well your PPC campaign is converting.
Assign goals that represent business value (i.e. A subscription completed, a payment processed, a user sign up...), and this will help you decide whether your money is being well-spent or not.
A big conversion factor to consider is the user experience of your website. Is it easy and clear for users to perform the actions they want to perform?
Are you effectively encouraging users to perform the actions you want them to perform?
Are those two goals balanced in a nicely-designed, trustworthy and secure platform?
And all the rest...
Once you've got your conversion process working nicely, then there's all sorts of things you can do to optimize your PPC campaign.
The main objective is to get away with paying less for each click, while maintaining the same volume and quality of traffic.
How?
Here's some ideas:
- Play around with bids and position. Being number 1 isn't always the best. Or position 11 might have a higher CTR than position 3...
- Increase CTR, whatever it takes. Ads that get clicks are deemed more relevant. The more relevant your ad, the less you'll theoretically have to pay to display it.
Split test ad copy (Google Adwords has a system for handling that), experiment with alternative keyword targeting, and track everything so that you have the stats to make an informed decision. - Optimize your site. Bounce rate and time on page will help Google judge what kind of experience you are offering users. If they go to your site and never come back, Google will take this as a signal that your ad is highly relevant to this search term or display context, and will be more likely to improve your keyword score.